<script>
  window.onload = function () {
    const winW = window.innerWidth || document.body.clientWidth
    const btn = document.getElementById('btn')

    let btnTop = '<%= btnTop %>';
    const EXP_PX = /(\d+|\.)px/.exec(btnTop)

    if (btnTop.indexOf('%') > 0) {
      btn.style.top = btnTop
    } else if (EXP_PX) {
      let num = Number(EXP_PX[1])
      const scale = winW / 750
      num = num * scale
      btn.style.top = num + 'px'
    }
  }
</script>
